Production of chromium oxid.



No. 65l,396. Patented lune l2, I900. E. A. G. STREET.

Pnonucnon 0F CHROMIUM oxm. (Application filed July 8, 1899.)

(No Model.)

THE NORRIS FETERS cu. Paoroufo. wnsmucn'on. 0, Q

' NITED STATES PATENT FFICE.

PRODUCTION OF CHROMI UM OXID.

'srncr'r 'roatrron forming part of Letters Patent No. 651,396, dated June 12, 1900.

Application filed July 8, 1899. Serial No. 723,235. (No s ecimens.)

To aZZ whom it may concern."

Be it known that I, ERNEST AUGUSTE GEORGE STREET,e11gineer, a resident of Paris, in the Republic of France, have invented a new and useful Improvement in the Production of Chromium Hydroxid, which is fully set forth in the following specification.

The production of chromium hydroxid by electrolysis from solutions of alkaline chromates or bichromates with or without porous partitions demands certain special conditions in order to obtain a good output.

When, for instance, a solution of alkaline metal chromate is electrolyzed cold with platinum electrodes, a very considerable expenditure of energy produces only small quantities of hydroxid. When the operation is carried on at or Centigrade with like electrodes, the output is small, although the conductivity of the electrolyte is increased by the elevation of temperature. If for the platinum cathode be substituted one of mercury while the temperature is maintained at 70 or 80 centigrade, the formation of chromium hydroxid is at once observed suspended in the electrolyte. The reaction goes on Well and quickly, being favored by the nature of the cathode and by the circulation of the liquid due to its temperature and the evolution of gas bubbles from the surface of the mercury cathode. By employing sodiumchromate solution the whole of the chromium can be precipitated as hydroxid under these conditions. The exhaustion is quite complete, the color of the electrolyte, which was at first yellow, becoming gradually modified, to become at last a colorless liquid which is a more or less concentrated alkaline solution, according to the strength of the chromate solution in the first instance. If bichromate be substituted for chromate, the final result is the same. After a time there remains only the chromium hydroxid instead of the chromate, and finally the electrolyte becomes colorless, being an alkaline solution, all the hydroxid being suspended in the liquid.

Starting with a solution of chromate, according as the chromium hydroxid is produced, the bath can be fed with bichromate, which, with the liberated sodium hydrate, forms chromate, this supply being limited only by the degree of concentration of the lye or desired solution of soda. The bichromate solution can also be circulated through a sucthe inlet are adjusted to the number of elec trolyzers, so that the liquid is rendered quite colorless. The separation of the chromium hydroxid from the soda solution is effected by decanting after quiescence or in any other way. The hydroxid is'then washed to free it as much as possible from alkali.

The precipitating agent is not the hydrox'id of the alkali metal,which would yield nothing, but the alkali metal itself, which is to be found on the cathode in the shape of an amalgam. With a cathode of mercury there is produced at this electrode an amalgam of sodium or potassium when a chromate or a bichromate is electrolyzed. This amalgam then reacts on the solution constituting the electrolyte in order to give hydroxid of chromium. When the work is done at a temperature of 70 or 80 centigrade, the combination heat furnished by the oxidation of sodium is sufficient to. produce hydrated oxid, insoluble in sodium or potassium hyd roxid in excess at the end of a certain time. This can only be obtained when a cathode of mercury is .used.

The reaction when sodium chromate is employed may be expressed as follows:

Instead of a platinum anode combined with a mercury cathode mercury can be used for both electrodes, in which case insoluble mercury chromate is formed on the anode. This mercury chromate can be transformed into oxid of chromium and mercury by reversing the direction of the current.

Briefly, the use of reversed currents under suitable conditions effects transformation of all the acid of the chromate into chromium hydroxid.

Whatever be the anode employed, the use of the mercury cathode alone decides the i11- crease of output by the process and constitutes the essence ofthis process.

The accompanying drawings illustrate apparatus such as hereinbefore referred to.

In Fig. 1, A is a vessel made of conducting material. B is the mercury cathode, and C the anode. D is an envelop about the vessel A, through which a hot liquid may be circulated to maintain the contents of the vessel at the proper temperature. A similar envelop may be provided for the apparatus shown in the other figures.

In Fig. 2, E is a Vessel of insulating material. ductor f leads. which conductor g leads.

F is a mercury cathode to which con- G is a mercury anode to Electrodes f and g are surrounded by tubes a: at of a suitable insulating material, such as glass.

Fig. 3 shows a series of electrolyzers similar to that of Fig. 1 (without the envelop) and connected by overflow-pipes H.

I claim The process of manufacturing chromium hydroxid from a solution of an alkali metal chromate or bichromate consisting in passing an electric current from a suitable anode through said solution to a mercury cathode while the temperature of the solution is maintained at about 70 centigrade.

In testimony whereof I have signed this specification in the presence of two subscrib ing witnesses;

ERNEST AUGUSTE GEORGE STREET;

Vitnesscs EMILE LEOBRET, EDWARD P. MAOLEAN. 

